(1) Technical Field
The present invention relates to a composition of liquid graphite. More specifically, the present invention relates to a composition of carbon powder, solvent and adhesive that can be used in a writing instrument, completely erased, and applied with a consistency, accuracy and darkness equivalent to that of a standard graphite pencil.
(2) Description of Related Art
Graphite pencils enjoy wide use and provide distinct advantages in writing and marking. Although functional, traditional pencils have several drawbacks. Pencils require constant sharpening where, after being dulled, they must be re-sharpened. Additionally, the graphite core is subject to breaking. In some circumstances, when the graphite core breaks, the pencil becomes virtually useless with the graphite simply falling out of the pencil.
As an alternative to a pencil, an ink pen may be used. An ink pen generally comprises an elongated barrel with an ink cartridge and a ball point tip. Although an ink pen does not need to be sharpened and does not break, it does have some inherent drawbacks. For example, when applied to paper, ink is subject to smearing and bleeding. Additionally, because the ink is absorbed into the fibers of paper, most inks are non-erasable.
To overcome problems associated with ink and to gain the benefits of graphite pencils, several forms of liquid graphite have been devised. U.S. Pat. Nos. 2,715,388; 2,852,397 and 2,956,038, issued to Cofield et al., Goessling, and Juelss et al., respectively, disclose forms of liquid graphite. However, existing liquid graphite compositions have several limitations. Many liquid graphite compositions are primarily liquid with only small concentrations of graphite, and rely on the absorption of the liquid and dissolved graphite into a porous writing surface such as paper to leave a mark. This process embeds the graphite within the writing surface and prevents it from being erased. Some existing liquid graphite compositions add darkening agents such as black ink in order to produce a darker mark, which further prevents the mark from being erased. Additionally, writing instruments using existing liquid graphite compositions suffer from pooling during application to a writing surface and leave an inconsistent, spread-out pattern of graphite as the liquid absorbs into the paper. Most existing liquid graphite compositions do not meet the standard graphite ratings for darkness and cannot be considered a “No. 2” equivalent, the established graphite hardness rating for standardized testing. Furthermore, a marking made with an existing liquid graphite solution is difficult to photocopy or scan into an electronic format.
Therefore, a need exists in the art for a composition of liquid graphite that is erasable and capable of being applied in a solid, dense marking that is suitable for use in standardized tests and for photocopying or scanning.